01
Dec
Study Confirms Connection Between Exposure to Pesticides and Male Reproductive Problems
(Beyond Pesticides, December 1, 2023) Even though researchers have noted since the 1970s that human fertility appears to be declining globally, doubt is still circulating that it is really happening and that pesticides could have anything to do with it. Very recently published studies, however, make it clear that, even without exact elucidation of the mechanisms by which pesticides damage male fertility, there is an unmistakable association of pesticides and many aspects of male reproductive health.
One of the new studies, a meta-analysis of 25 studies on the connection between pesticides and male reproductive problems, finds that men exposed to organophosphate (such as glyphosate and malathion) and carbamate (such as carbaryl and methiocarb) insecticides have lower sperm concentrations than the general population. This is especially true of men exposed in work settings. The senior author of the study, Melissa J. Perry,ScD of the George Mason University College of Public Health, told HealthNews, “The evidence available has reached a point that we must take regulatory action to reduce insecticide exposure.”
Human infertility is defined as “the failure to achieve pregnancy after 12 months or more of regular unprotected sexual intercourse.” Most public attention regarding infertility focuses on women’s difficulties in getting pregnant, causing couples to resort to in vitro fertilization and surrogates. But about a third to half the time, a couple’s infertility results from problems with the male contribution. Men’s reproductive health is measured by total sperm count, sperm’s ability to move, the incidence of malformed sperm or reproductive organ structure, testosterone levels and other criteria.
The relationships between aspects of male reproductive health such as sperm count, fertility and testicular cancer are not perfectly understood, but they are known to be interrelated. Low sperm counts can not only indicate decreased fertility, but also correlate with other markers of declining male reproductive health, including testicular tumors and testosterone levels. In 2017 Shanna Swan, PhD of the Icahn School of Medicine at Mount Sinai and colleagues published a major review of changes in sperm count between 1973 and 2011. They found that sperm counts declined by 52.4 percent over their study period.
Swan et al. also noted that reduced sperm count is a strong predictor of overall disease and death risk. In other words, sperm count reflects influences on health that go far beyond reproduction, and also that reproductive health is created by proper hormone balance, which many pesticides are well known to disturb.
Dr. Swan and colleagues wrote that chemical exposures, including pesticides (especially the endocrine disrupters) are plausible bad actors in the sperm count decline, but also said “lifestyle factors” such as diet and smoking are likely factors. High body mass index (BMI) and obesity have also been associated with low sperm counts.
Obesity is often cited as a “lifestyle choice” causing the reproductive problems, unrelated to factors like pesticide exposures. This is something of a straw man, however, because obesity itself can be an outcome of such exposures. For example, a 2022 review found that two carbamate insecticides and eight organophosphate insecticides were “significantly associated with higher obesity prevalence,” suggesting that obesity and low sperm count may have a common cause rather than a direct cause-and-effect relationship.
Pesticides present an especially vexing problem in that they affect organisms through many different pathways, often simultaneously. For example, organophosphates notoriously damage neurotransmitters, but they have also been associated with poor semen quality in exposed factory workers. Similarly, carbamates interfere with neurotransmitters and are known for disrupting thyroid and steroid hormones and increasing the risk of both non-Hodgkin’s lymphoma and dementia, but they have also been associated with chromosome damage in sperm. Far less scientific attention has been devoted to these chemicals’ effects on male reproduction than on their neurological ones, but the reproductive consequences may be even greater. For one thing, many pesticides, including organophosphates, can cross the placental barrier if the mother is exposed during pregnancy. Fetal exposures to organophosphates affect childhood cognition and coordination and predispose the child to develop cancer in later life.
But it gets worse. A father’s environmental exposures can alter not only his direct fertility but also his epigenetic patterns, and these can be passed from parent to child. Epigenetics are a suite of cell processes in which gene expression is controlled by molecules that block or open access to genes in the double DNA helix. In every cell of the body, this process continually operates to orchestrate the cell’s biochemistry and its relation to other cells and organs, but it does not change genes themselves. Epigenetic patterns are a kind of template or history of the habits and exposures of the parent, including smoking history, diet, pesticide exposures, alcohol and drug consumption, and social stress. Sperm are major contributors of epigenetic information passed from one generation to the next, and pesticides affect that information.
“It is becoming clear that epigenetic information can function as molecular memory of past environmental exposures and be passed from one generation to another via the germline,” according to the authors of a 2022 review by a pair of Georgetown University Medical Center and Lombardi Comprehensive Cancer Center scholars. Descendants of an exposed male may have no direct exposure themselves but be paying for the inadvertent “sins” of their fathers—“sins” such as agricultural or factory work.
A 2023 update of the 2017 review of temporal trends in sperm count, also co-authored by Swan, expanded the geographical range of the study by including data on men in 53 countries on six continents to get a global picture rather than one focused on industrialized countries where data is more plentiful. They found “strong evidence” that sperm counts have declined globally. Disturbingly, the authors show that the downward trend in sperm counts has become steeper since 2000, accelerating beyond the already-worrisome rate seen in the 2017 meta-analysis. From 1972 to 1999, sperm count dropped by about one percent a year; since 2000, the rate has been about 2.6 percent.
The evidence has continued to mount that pesticides affect both male and female reproductive health, yet most of these chemicals remain on the market, contributing to the prospect of agricultural collapse and declining human population worldwide. There is no longer any time to waste. What Beyond Pesticides said in 2022 still holds: “As the human civilization grapples with a range of cascading crises, from climate change to the insect apocalypse and global biodiversity crisis, we may be missing the chance to address one of the most critical aspects to the continuation of humanity as we now know it.”
For more information on the fertility crisis, see Dr. Swan’s presentation to Beyond Pesticides’ 2021 National Pesticide Forum, Cultivating Healthy Communities, on Beyond Pesticides’ YouTube page.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
Sources:
Temporal trends in sperm count: a systematic review and meta-regression analysis https://pubmed.ncbi.nlm.nih.gov/28981654/
Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries
https://academic.oup.com/humupd/article/29/2/157/6824414?login=false
Pesticides and Male Fertility: A Dangerous Crosstalk
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8707831/
Paternal Transmission of Stressed-Induced Pathologies
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3217197/
Scientific Literature Review Again Connects Pesticides and Male Fertility Problem
Scientific Literature Review Again Connects Pesticides and Male Fertility Problems
Sperm counts worldwide are plummeting faster than we thought
https://www.nationalgeographic.co.uk/science-and-technology/2022/11/sperm-counts-worldwide-are-plummeting-faster-than-we-thought
The Sperm-Count ‘Crisis’ Doesn’t Add Up
https://www.nytimes.com/2021/06/04/health/sperm-fertility-reproduction-crisis.html
